1. Field of the Invention
The invention relates to a short arc discharge lamp which is used as a light source for a projector, for semiconductor exposure, for UV curing and the like.
2. Description of the Prior Art
Conventionally, a xenon gas-filled short arc lamp is used, for example, for a light source for a projector. Recently, there has been more and more often a high demand for more radiance of the projected image of the projector. Therefore, there is the tendency to increase the amount of added xenon gas. As a result, the gas pressure in the arc tube of short arc lamps during operation, recently, has been extremely high.
In one such short arc lamp, a spherical or oval arc tube composed of silica glass is filled with xenon gas along with opposed cathode and anode electrodes. The upholding parts of the cathode and anode electrodes are sealed in ends of side tubes which adjoin opposite sides of the arc tube. To secure the upholding parts of the electrodes of the cathode and the anode, the ends of the side tubes are contracted by heating, the diameter is reduced, and thus, contracted areas are formed. However, in order to directly secure the upholding parts of the cathode and anode electrodes in the contracted areas of the side tubes, the amount of contraction must be increased.
Therefore, the upholding parts of the cathode and anode electrodes are inserted into a silica glass holding cylinder, the contracted areas of the side tubes are welded to the holding cylinders, and thus, the upholding parts of the cathode and anode electrodes are secured.
If the contracted areas of the side tubes are welded to the holding cylinders, on the weld end, a wedge-like area is formed as a small gap which leads to the formation of fractures during operation. Therefore, as can be seen from Japanese patent disclosure document HEI 11-135067 and corresponding U.S. Pat. No. 6,356,018, an arrangement is suggested in which in the outside periphery of the respective holding cylinder, there is an intermediate layer in the form of a metal layer or ceramic layer.
FIG. 1 shows as the prior art a short arc discharge lamp in a schematic cross section in which the technology described in the above described publication is used. Here, there are an anode 22 and a cathode 21 in the oval arc tube 10. Bordering the arc tube 10, there are side tubes 11 into which the upholding parts 23 of the electrodes are inserted; on their respective tip, an electrode is mounted and they are sealed on the ends of the side tubes. Thus, on the respective end of the side tube, a sealed area 13 is formed. The upholding parts 23 of the electrodes are each inserted into a holding cylinder 30 of silica glass for securing the upholding parts of the electrode and secured. The outside periphery of the respective holding cylinder 30 is provided with an intermediate layer 40 in the form of a metal layer or a ceramic layer.
However, since the contracted area 12 of the side tube and the holding cylinder 30 are not welded to one another, there is the danger that the holding cylinders 30 will move if, during transport or the like, the lamp is subjected to vibration. If the holding cylinders 30 move, the force is concentrated on the sealed areas 13; this leads to lamp damage.
The primary object of the invention is to devise a short arc lamp in which the glass tubes of the holding cylinders are prevented from moving, the force acting on the lamp is prevented from being concentrated on the sealed areas and the lamp is prevented from being damaged when the lamp is shaken during transport or the like.
In a first aspect of the invention, in a short arc discharge lamp in which in the arc tube there are opposed cathode and anode electrodes, in which the upholding parts of the cathode and anode electrodes are each secured by insertion into a holding cylinder, in which these holding cylinders are supported by contracted areas of the side tubes which adjoin the arc tube, and in which the outer periphery of the respective holding cylinder is coated with a coating material of metal or ceramic, the object is achieved by the respective holding cylinder having a part with a reduced diameter in the lengthwise direction.
The object is achieved according to one development of the invention by the holding cylinders having an outside diameter which decreases in the direction toward the cylinder middle and the holding cylinders are preferably shaped essentially like a tambourine.
The holding cylinders can, moreover, have several sections of reduced diameter in the lengthwise direction so that the holding cylinders, for example, have an outside contour with a wave shape in the lengthwise direction.
According to another aspect of the invention, in a short arc discharge lamp in which in the arc tube contains opposed cathode and anode electrodes, in which the upholding parts of the electrodes of the cathode and anode electrodes are each secured by insertion into a holding cylinder, in which these holding cylinders are supported by contracted areas of the side tubes which adjoin the arc tube, and in which the outer periphery of the respective holding cylinder is coated with a coating material of metal or ceramic, the object is achieved by the outside peripheral surface of the respective holding cylinder being provided with projections. For example, the holding cylinders can have flange-like projections on their respective ends.
The holding cylinders can have both a round-cylindrical and also a polygon-cylindrical basic shape.
The invention is described specifically below using several embodiments shown in the drawings.